Such power tools are mobile, manually guided, pneumatically driven and require a supply of a lubricant to the cutter when the power tools are in operation. Such operations include, for example drilling, reaming, countersinking of bores, and the like. Such power tools comprise a mobile feed advance unit and are widely used in aircraft construction. The lubricant is primarily a mixture of lubricating oil and pressurized air. During operation the lubricating oil-air mixture is fed from a supply container to the cutting location where a cutter, such as a drill bit, a reamer or any other material removing tool engages a workpiece. The oil discharged from a supply container during operation of the tool is replenished when the power tool is not in operation.
German Patent Publication DE 43 39 770 A1 discloses a mobile precision drilling power tool that can be locked in a fixed position at a drilling location of large work pieces. The conventional power tool is constructed for precision drilling operations whereby a liquid lubricant is supplied all the way to the cutting tool edges. The known drilling power tool has a tool spindle carrying a chuck. The spindle is driven to rotate and for an axial feed advance of the spindle. The flow of lubricant passes through the spindle.
Conventional tools of the type described above have certain disadvantages or drawbacks such as an inadequate performance particularly when the lubricant supply system must also feed air to the cutting location. Another drawback is seen in that the dosing adjustment is inadequate so that either too much or too little lubricant is supplied to the cutting location. Moreover, the supply of lubricant takes place in cycles rather than continuously in response to constant process parameters. Further, conventional lubricating devices are constructed with a particular power tool or machine tool in mind and thus require an adaptation when a use for other power tools is intended. Frequently, such adaptation is not possible with regard to certain or even any power tools. Still another drawback of conventional lubricating tools is seen in that different drilling and friction conditions cannot be fully satisfied when a power tool is used in different operating positions such as horizontal and vertical drilling operations. Still another drawback is seen in that the lubricant reaches the cutting location only after a rather long reaction time following the activation of the lubricating tool.